July 16, 2013

Insights Into The Possible Origins Of Hot Flashes In The Brain

For the first time in years, neuroscientists from Wayne State University School of Medicine have provided novel insights into the neural origins of hot flashes in menopausal women. The study, published in Cerebral Cortex, might inform and eventually lead to new treatments for women experiencing the sudden but temporary episodes of body warmth, flushing and sweating.

"The idea of understanding brain responses during thermoregulatory events has spawned many studies where thermal stimuli were applied to the skin. But hot flashes are unique because they are internally generated, so studying them presents unique challenges," said Robert Freedman, PhD, professor of psychiatry and behavioral neurosciences, founder of the Behavioral Medicine Laboratory and a member at the CS Mott Center for Human Growth and Development. "Our participants had to lie in the MRI scanner while being heated between two body-size heating pads for up to two hours while we waited for the onset of a hot flash. They were heroic in this regard and the study could not have been conducted without their incredible level of cooperation."

Vaibhav Diwadkar, PhD, associate professor of psychiatry and behavioral neurosciences, added, "Menopause and hot flashes are a significant women's health issue of widespread general interest. However, understanding of the neural origins of hot flashes has remained poor. The question has rarely been assessed with in vivo functional neuroimaging. In part, this paucity of studies reflects the technical limitations of objectively identifying hot flashes while symptomatic women are being scanned with MRI. Nothing like this has been published because this is a very difficult study to do."

Over the course of a single year, study participants were scanned at the School of Medicine's Vaitkevicius Imaging Center, located in Detroit's Harper University Hospital. The 20 participants were healthy, symptomatic postmenopausal women ages 47 to 58 who reported six or more hot flashes a day.

The team collected skin conductance levels - which is an electrical measure of sweating - to identify the onset of hot flashes while the women were being scanned. The participants were connected to a simple circuit that passed a very small current across their chests. Monitoring the changes in levels allowed researchers to identify a hot flash onset and analyze the concurrently acquired fMRI data to investigate the neural precedents and correlates of the event.

Certain regions of the brain were the focus of the study. For example, the team focused on the brain stem because its sub regions, the medullary and dorsal raphe, are implicated in thermal regulation. Forebrain regions, like the insula, have been implicated in the personal perception of how someone feels. The scans revealed activity in some brain areas, such as the brain stem, begins to rise before the actual onset of the hot flash.

"Frankly, evidence of fMRI-measured rise in the activity of the brain stem even before women experience a hot flash is a stunning result. When this finding is considered along with the fact that activity in the insula only rises after the experience of the hot flash, we gain some insight on the complexity of brain mechanisms that mediate basic regulatory functions," Diwadkar said.

The study findings point to possible origins of hot flashes in specific regions of the brain. The team believes this is the first demonstration of such findings in the academic literature.

The researchers are currently evaluating the network-based interactions between the brain regions using the more complex modeling of functional magnetic resonance imaging (fMRI) data. "We think that our study highlights the value of using well-designed fMRI paradigms and analyses in understanding clinically relevant questions," Diwadkar said.

They are also exploring the possibility of integrating imaging with treatment to determine whether specific pharmacotherapies for menopause might alter regional brain responses.